Revert 251503 "Implement inline signin with iframe"

chrome/browser/resources/gaia_auth/inline_injected.js

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * @fileoverview Code injected into Gaia sign in page for inline sign in flow.
  * On load stop, it receives a message from the embedder extension with a
  * JavaScript reference to the embedder window. Then upon submit of the sign
  * in form, it posts the username and password to the embedder window.
  * Prototype Only.
@@ skipping 26 matching lines @@
                chooseWhatToSync: chooseWhatToSync};
 
     extWindow.postMessage(msg, 'chrome://chrome-signin');
     console.log('Credentials sent');
 
     return;
   };
   // Overrides the submit handler for the gaia login form.
   gaiaLoginForm.onsubmit = onLoginSubmit;
 })();